Advances in magnetic resonance imaging (MRI) are driving the development of faster and higher resolution MRI machines. While MRI machines with static magnetic fields of 1 to 2 tesla (T) and resolutions of 2 mm3 are standard in clinical use, higher resolution requires stronger fields. Little is known about the sensory or physiological effects of static magnetic fields of high strength on mammals and humans. Using the large- bore, high-strength NMR magnets at the U.S. National High Magnetic Field Laboratory at Florida State University, we have discovered that exposure to 7T or higher magnetic fields has behavioral and neural effects on rats. At the behavioral level, magnetic field exposure induced a conditioned taste aversion after pairing with the taste of saccharin. At the neural level, the same exposure induced specific and significant c- Fos , a marker of neuronal activation, in the rat brainstem. c-Fos was observed in visceral and stress relays and in vestibular nuclei (e.g. the medial vestibular nucleus). Both the behavioral response and the pattern of c-Fos activation are similar to the effects of vestibular disturbance, such as rotation and motion sickness. In the previous funding period, labyrinthectomy was found to block all these effects;the specific inner ear organ responsible for magnetic field transduction is still unknown, however. Two other notable findings were: 1) preexposure to 14T reduces responsiveness upon later exposure, suggesting either sensory adaptation or damage;2) after rats are trained to climb a ladder through the 14T magnet, they not only refuse to traverse 14T on subsequent trials, but they will not cross the 2T field line. Here we propose: to explore the specific vestibular sites that transduce magnetic field reponses using using pharmacology and mutant mouse strains that lack otolith or semicircular organs;to define the parameters of preexposure that may distinguish adaptation from damage;and to determine the thresholds for aversion and detection using a) ladder-climbing through different magnetic fields and b) conditioned suppression with magnetic fields as the cue. This proposal is relevant to public health in two ways: First, patients undergoing MRI examinations are routinely exposed to high strength static magnetic fields of 3T, and higher strength MRI machines are in development. This proposal explores the effects of similar magnetic fields on the vestibular system that might cause acute motion sickness or long-term changes in vestibular function after repeated exposure. Secondly, vestibular dysfunction is a common complaint and cause of injury (e.g. falling in the elderly), and this proposal contains novel approaches to investigating the inner ear and vestibular system